Dimerization process



DIMERIZATION PROCESS Charles E. Frank, Cincinnati, Ohio, and Walter E. Foster, Baton Rouge, La., assignors to National Distillers and Chemical Corporation, a corporation of Virginia No Drawing. Application September 25, 1953, Serial No. 382,456

14 Claims. (Cl. 260-533) This invention relates broadly to a novel process for the preparation of dimerized products from dienes and to the compositions obtained thereby and, more specifically, relates to a process wherein conjugated aliphatic diolefins are selectively reacted to give high yields of dimerized derivatives relatively free from more highly polymerized products.

This application is a continuation-in-part of application Serial No. 333,354 filed January 26, 1953.

It is an object of this invention to react aliphatic conjugated diolefins selectively with an alkali metal such as sodium or potassium in finely dispersed form to obtain the dimetallo derivatives of dimerized dienes having twice the number of carbon atoms of the starting diolefins.

Another object of this invention is to carry out a subsequent step by carbonating the dimetallo derivatives so obtained to form the salts of dicarboxylic acids derived from the dimerized dienes and having two additional carbon atoms. The resulting salt products may be converted to acids and the latter isolated, or the salt products may be separated as such and then converted to acids.

A further, more specific object is to selectively dimerize butadiene using finely dispersed sodium and in the presence of an ether reaction medium and a small amount of a polycyclic-aromatic hydrocarbon to obtain disodiooctadienes and, if desired, thereafter to carbonate said product to obtain aliphatic C dicarboxylic acids and salts thereof.

It has been heretofore proposed to prepare mixtures of organic acids by reacting an aliphatic diolefin such as butadiene with sodium or potassium and carbon dioxide in a special solvent and to hydrolyze the compounds so obtained. In this prior work, the sodium was used in massive form, with provision for an abrading or scraping of the sodium surfaces with a rotating brush or scraper. Experimental studies of the products so obtained show that they are complex mixtures of polymeric acids having a range of relatively high molecular weights. Large quantities of polymers of the Buna rubber type are also produced. These materials have relatively little industrial value, and are entirely different from the selectively dimerized products obtained by this invention.

The present invention is carried out by initially treating an aliphatic conjugated diolefin with finely dispersed sodium or potassium in the liquid ether medium and in the presence of a relatively small amount of a polycyclic aromatic hydrocarbon at a temperature below C.

The disodiodiene product thus obtained is then carbonated at a temperature below 0 C., to give the salts of the desired dicarboxylic acids in high yields and selectivity.

The net result of the initial step is a reaction which yields a dimerized product. In the case of sodium and butadiene, this product comprises the disodium derivatives of the aliphatic octadienes. From a study of structures of the saturated diacids arising therefrom, it has nited States Patent I 2,816,916 Patented Dec. 17, 1957 'ice Using the herein described selective process, it is possible to obtain combined yields of the above C dimerized products ranging up to -90%based on the butadiene.

Subsequent carbonation of the above disodium derivatives, followed by hydrogenation and acidification, yields, respectively, sebacic acid, Z-ethylsuberic acid, 2,2'-diethyl adipic acid, and S-ethylsuberic acid.

The diolefins which are useful for this improved process include any aliphtic conjugated diolefin such as, for example, butadiene, isoprene, dimethyl butadiene, the pentadiens, as the methyl-1,3-pentadienes, and the like. In general, it is desirable to use the conjugated diolefins having from 4 to 8, inclusive, carbon atoms. The meth- 001 is particularly well adapted to the use of butadiene as the diolefin.

Either sodium or potassium may be used as the alkali metal reactant. The use of sodium is preferred over potassium since sodium gives'excellent selectivity and yields of dimerized products, and it is cheaper and more readily available. Chemically pure sodium is not essential, however, since mixtures containing a major proportion of sodium are also useful. Thus, alloys of sodium and potassium, sodium and calcium, and sodium and lithium can be used.

One factor essential to the successful production of the dimerized derivatives is the use of the alkali metal in finely dispersed form. A sodium dispersion in which the average particle size is less than 50 microns is necessary for satisfactory dimerization since bulk sodium instead of dispersed sodium either yields no product or results largely in the formation of highly condensed diene polymers. The formation of these unwanted polymeric products as the major reaction product can be substantially avoided by employing the sodium or potassium as a fine dispersion. This dispersion is most conveniently made in an inert hydrocarbon or ether as a separate step preliminary to the reaction with the diene.

The reaction medium found most suitable consists essentially of an ether and only certain types of ethers are effective. These particular classes of ethers have the common property of serving as promoters of the diolefin dimerization. The ether can be any aliphatic mono ether having a methoxy group, in which the ratio of the number of oxygen atoms to the number of carbon atoms is not less than 1:4. Examples include dimethyl ether, methyl ethyl ether, methyl n-propyl ether, methyl isopropyl ether, and mixtures of these methyl ethers. Certain aliphatic polyethers are also quite satisfactory. These include the acyclic and cyclic polyethers which are derived by replacing all of the hydroxyl hydrogen atoms of the appropriate polyhydric alcohol by alkyl groups. Typical examples are the ethylene glycol dialkyl ethers such as the dimethyl, methyl ethyL diethyI, methyl butyl, ethyl butyl, dibutyl, and butyl lauryl ethylene glycol ethers; trimethylene glycol dimethyl ether, glycerol trimethyl ether, glycerol dimethyl ethyl ether, and diethylene glycol methyl ethyl ether, dioxane, glycol formal, methyl glycerol formal, and the like, as well as ethyl and methyl ortho formates, methylal and acetals having the proper carbon to oxygen ratio. The simple methyl monoethers, as dimethyl ether, and the polyethers of ethylene glycols, as ethylene glycol dimethyl ether are preferred. Hydrocarbon solvents such as isooctane, kerosene, toluene, and benzene cannot be used exclusively as reaction media since they adversely affect the dimerization reaction and give little or no yield of dimer products.

The ethers should not contain any groups such as bydroxyl, carboxyl and the like which are distinctly reactive towards sodium. Although the ether may react in some reversible manner, it must not be subject to cleavage to give irreversible reaction products during the dimerization process. Such cleavage action destroys the ether and introduces into the reacting system metallic alkoxides which, in turn, tend to induce the rubber forming reaction with the diolefin rather than the desired dimerization reaction.

Although the reaction medium should consist essentially of the specified ethers other inert media can be employed in limited amounts. In general, these inert media will be introduced with the sodium dispersion as the liquid in which the sodium is suspended. They have the principal effect of diluting the ethers. As the effective concentration of the active ether is decreased by the increased addition of inerts, a minimum concentration of ether is reached below which the promoting effect is not evident. The exact minimum concentration depends upon the particular reactants and ether being used as well as the reaction conditions, such as temperature, reactant concentration, and the like employed. In any event, the concentration of ether in the reaction mixture should at all times be maintained at a sufficient level to have a substantial promoting eifect upon the dimerization reaction. In general, it is good practice to use a reaction medium having at least 50 wt. percent of active ether. Although the amount may be varied considerably, from 100 to 2000 cc. of the ether per mole of diolefin undergoing reaction has been found satisfactory.

It is further necessary to include in the dimerization reaction mixture a relatively small amount of at least one compound of the polycyclic aromatic class. By this term it is intended to include condensed ring hydrocarbons such as naphthalene and phenanthrene, as well as the uncondensed polycyclic compounds such as diphenyl, the terphenyls, dinaphthyl, tetraphenyl ethylene and the like. It is also intended to include mixtures of these compounds. The polyphenyl compounds such as diphenyl and the terphenyls and their mixtures have been found to be particularly useful. The amount of the hydrocarbon required will vary over a range which in every case will be relatively small in comparison with the amount of diolefin undergoing reaction. The exact amount in any particular reaction will depend on temperature, time of reaction and the structure of the diolefin. Concentrations in the range of 0.1 to wt. percent based on the amount of diolefin are ordinarily quite sufiicient.

The activation effect which these polycyclic aromatic hydrocarbons show is apparent both in the greatly increased selectivity of the diolefin dimerization as well as the increased speed of the reaction.

These active hydrocarbons have the property of yielding highly colored sodium hydrocarbon addition products in the presence of the active ether employed. While the exact role played by such materials is not fully understood and it is not desired to limit the process to an exact theory, they can be regarded as chemical activating agents which, in effect, have the property of transferring metallic sodium to the diolefin in the reaction zone, facilitating its passage through a film of sodium reaction product which would ordinarily effectively isolate the sodium from reagents present in solution in the surrounding medium. However, the addition of butadiene to an ether solution of sodium-terphenyl in the absence of metallic sodium yielded little or no dimerized butadiene products, but only condensed ring products derived from terphenyl. Therefore, this process is not equivalent to the use of a metallic derivative'of the polycyclic aromatic compound as the dimerization agent.

It is a further requirement in the process that the reaction temperature preferably be held below 0 C. The temperature range between -20 to --50 C. is the preferred one. Generally speaking, all ethers begin to yield cleavage products at temperatures of about 0 C. and above, with the result that sufiicient alkoxides are formed to yield high polymeric acids rather than the desired low molecular weight disodio-diolefin dimers.

The reaction may be carried out in a stirred reaction vessel. In one typical method for carrying out the invention, the sodium or potassium dispersion is initially prepared by placing an inert hydrocarbon such as isooctane in a suitable vessel with the appropriate weigh-t of sodium. Using finely dispersed sodium it is only necessary to employ an equimolar amount with the butadiene to be reacted. Although a slight excess may be added, it is unnecessary and it is desirable to have no unconsumed metal remaining at the end of the reaction period. The mixture is heated in a surrounding bath or otherwise until the sodium has melted (M. P. 97.5 0). Then a suitable high speed agitator is started and, preferably, an emulsifier consisting, for example, of /2 (based on sodium) of the dimer of linoleic acid is added. After a short period of agitation, a test sample of the dispersion shows the particle size to be in the 5-15 micron range. The stirring is stopped and the dispersion is allowed to cool to room temperature. This dispersion is now ready to be used in the selective dimerization of diolefins. Inert liquids such as saturated dibutyl ether, normal octane, n-heptane, or straight run kerosenes, may be employed as suspension media for the dispersion. Any such dispersion having sufficiently finely divided sodium or potassium will suffice. Other well-known substances may be used instead of the dimeric linoleic acid as the dispersing agents.

The dispersion is cooled to and maintained below 0 C. and the diolefin introduced either as a gas, or under pressure, in the liquid phase. One quite satisfactory method is to introduce the diolefin into the reaction vessel at approximately the same rate as that at which it reacts with the sodium.

This reaction may be carried out either in a batchwise or in a continuous manner and it is not intended to limit the process to any particular method of operation.

The dimetallic derivatives of the diolefin dimers which are selectively formed are thus produced in the reaction mixture. These products, depending on the diolefin, may be either soluble or insoluble in the reaction medium. In general, they tend to form slurries, as for example, the disodiooctadiene produced from sodium and butadiene.

It is believed that these dimetallic derivatives are in themselves novel and it is intended to claim them as new compositions of matter. They can either be isolated as such, or, since they tend to be unstable and diflicult to handle, they can be directly and immediately thereafter subjected to further reactions to form valuable derivatives. For example, subsequent carbonation of the mixture containing the products yields the salts of dicarboxylic acids. The carbonation may be done by subjecting the dimetallic-diene derivatives to dry gaseous carbon dioxide, by contact with solid carbon dioxide or by means of a solution of carbon dioxide. The temperature should be controlled below 0 C. to avoid the formation of unwanted by-products. This carbonation forms the dimetallic salts of the unsaturated aliphatic dicarboxylic acids. These. salts .will contain two more carbon atoms than the dimetallic diene dimers from which they are produced. In the case where butadiene is the starting aliphatic diolefin, there results by this method the selective production of C unsaturated dicarboxylic acids.

It is important when producing the diacids and their salts to carry out the dimerization and carbonation as two separate steps. The dimetallic diene dimer is first made and the carbonation is done as soon afterwards as possible. If carbon dioxide is present during the dimerization, the reaction is neither as selective nor as complete.

The diacid salts are water soluble and may easily be separated by a water extraction. Alternatively, they may be converted to the free acids by acidification and separated by filtration, evaporation and/or solvent extraction.

These unsaturated diacid products find use as chemical intermediates, and are valuable in the perparation of polymers and copolymers, plasticizers and drying oils. They are especially useful in esters and polyester and polyamide resins.

In addition, the unsaturated diacids or their salts or other derivatives can be hydrogenated at the double bonds to yield the corresponding saturated compounds, particularly the saturated diacids. This also affords a convenient and accurate way to identify structures of the intermediate products. For example, the disodiooctadiene product obtained from butadiene ultimately yields a practically quantitative mixture of sebacic acid, 2-ethyl suberic acid and 2,2-diethyl adipic acid. Traces of 3-ethyl suberic acid also may be present.

The invention will be described in greater detail by the following examples. These examples and embodiments are illustrative only, and the invention is not in any way intended to be limited thereto except as indicated by the appended claims. All parts are expressed as by weight unless otherwise specified.

EXAMPLE 1 Preparation of C diacids from butadiene The reaction was carried out in a stirred reactor having a gas inlet tube extending into the body of the reaction mixture and a reflux condenser vented to a nitrogen atmosphere. This reactor system was purged with nitrogen and charged with 1000 parts of dimethyl ether, 3 parts (about 1.8 wt. percent based on the butadiene used) of para-terphenyl and 69 parts of sodium dispersed in 70 parts of isooctane. The average particle size of the sodium was microns. A stream of gaseous butadiene amounting to a total of 162 parts was passed into the reactor over a 4-hour period While maintaining vigorous agitation and maintaining the reaction temperature at about C. During this period the disodium derivatives of the C butadiene dimers were formed.

After the butadiene addition was completed, the reaction mixture containing the disodium derivatives as a slurry was carbonated by pouring it upon an excess of solid carbon dioxide. After evaporation of excess CO dimethyl ether and isooctane, a solid product, consisting essentially of the sodium salts of the C unsaturated dicarboxylic acids remained. A small amount, less than 5%, of rubbery butadiene polymer was also isolated. An alkaline solution of the dicarboxylic acids was hydrogenated using a nickel catalyst.

The hydrogenated diacids were precipitated by addition of mineral acid. The combined yield of lO-carbon atom diacids was 67% based on the sodium. Separation and analysis of this mixture showed the following composition:

2,2-diethyladipic acid percent 8 2-ethyl suberic acid do 36 Sebacic acid do 23 B-ethyl suberic acid trace The individual acids were identified by their melting points.

The mixed terphenyls (ortho, meta and para isomers) can be satisfactorily substituted for the para-terphenyl of Example 1. Substantially the same results and products are obtained.

EXAMPLE 2 Preparation of C diacids from isoprene Substantially the same procedure as described above in Example 1 was repeated with the exception that 204 parts of isoprene was used as the conjugated diolefin instead of the butadiene. After reaction with finely dispersed sodium followed by carbonation and hydrogenation, the reaction product was found to contain C dicarboxylic acids in 64% yield based on the sodium.

EXAMPLE 3 Preparation of C diacids from methyl-pentadienes A further experiment was carried out following the procedure of Example 1 except that 246 parts of a mixture of 4-methyl-1,3-pentadiene and 2-methyl-l,3- pentadiene was used. The resulting reaction mixture yielded a mixture of C dicarboxylic acids in 56% yields based on the sodium.

EXAMPLE 4 Preparation of C diacids using sodium-calcium alloy The procedure of Example 1 using butadiene was followed except that 75 parts of a sodium-calcium (75:25) alloy was dispersed and used instead of 69 parts of sodium. A yield of 57% of C dicarboxylic acids based on the sodium was obtained.

EXAMPLE 5 Preparation of C diacids using sodium-lithium alloy The same procedure of Example 1 was again repeated using 75 parts of a sodium-lithium (:5) alloy instead of 69 parts of sodium. This procedure gave a 54% yield of C dicarboxylic acids based on the sodium.

EXAMPLE 6 Preparation of C diacids using para-terphenyl An experiment similar to Example 1 was carried out using substantially the same apparatus as that used in Example 1. The reactor was purged with nitrogen and charged with 320 parts of ethylene glycol diethyl ether and 2 parts of para-terphenyl (about 7.4 wt. percent based on the butadiene used). A dispersion of 25 parts sodium. in 50 parts of di-n-butyl ether, in which the sodium had an average particle size of 12 microns, was then added. A stream of butadiene totaling 27.1 parts was then passed into the reactor over a period of six hours while maintaining the temperature of the reacting mixture between 25 and 35" C.

After the addition of butadiene was completed, the reaction mixture was carbonated by pouring it onto an excess of crushed Dry Ice. Excess CO was allowed to evaporate and the mixture was treated with about 200 parts of water in a nitrogen atmosphere. The water and hydrocarbon layers were then separated. The oil layer was washed with dilute sodium carbonate solution, which was then added to the water layer. The organic acids were separated from the water layer by acidification with mineral acid. The crude acid so obtained amounted to about 68 parts by weight. This product was dissolved in 200 parts of diethyl ether and hydrogenated over a platinum catalyst to yield the corresponding saturated dicarboxylic acids.

After hydrogenation, a part of the sebasic acid precipitated from the ether solution. The remaining acid products were isolated by evaporating off the ether solvent, followed by filtration, petroleum ether extraction, and distillation under reduced pressure. The products had the following composition:

Parts sebacic acid 15.8 Z-ethylsuberic acid 20.8 3-ethylsuberic acid and 2,2'-diethyladipic acid 4.7

subsequent to the contacting of the sodium and butadiene, while in run 4, the carbonation was caried out simultaneously. Analysis of the product showed that there was only a trace (a maximum of about 2%) of distillable acids produced. The major part of the butadiene was These roducts re resent an 82 ield of C dicar- 9 boxylic agids based 2 the zz converted into hlgh molecular weight rubbery products. Runs 5 and 6 show the results obtained when the EXAMPLE 7 process of runs No. 1 through 4 was repeated in the prespreparation of C diacids using ortho terphenyl ence of a polycyclic aromatic hydrocarbon, para-teru 10 phenyl. The products were found to contain somewhat An experiment s1m1lar in every way t Example 6 increased percentages of distillable acids, but, when these was carmfd out s 2 Parts 9 ortho'terphenyl arld were fractionated and studied, they were found to consist Pa of dISPeTSPd Sodlum- A Yleld of 66% of 10 dlbaslc largely of high molecular weight acidic products. For exaclds was obtamedample, the result obtained in run No. 5 shows dicarboxylic EXAMPLE 3 products of 345 to 540.8 molecular weight (neutralization Preparation of C diacids using naphthalene equlvalent X assllmmg dlaclds)- The total Ylelds Of A th these polymeric acids ranged from 53.3% to 56.9%, E n expgnment was earned out ldentlcal with at of based on the butadiene. These results clearly show that no xamgle except that 2 parts of naphthalene was used selective dimerization has taken place t A 66% yleld of C10 dlcar' The great selectivity and other advantages obtained by oxy 16 am 8 resu using the herein described novel process are obvious from EXAMPLE 9 the data of runs 7 and 8. In these reactions finely dispersed sodium (less than 50 microns average particle size) Prepamnon of dmclds usmg tetmphenyl ethylene was employed in conjunction with small amounts of ter- The procedure and conditions of Example 6 were folphenyls as the polycyclic aromatic hydrocarbon. In each lowed using 2 parts of tetraphenyl ethylene instead of case, the reaction was carried out in two steps, the carbopara-terphenyl and 46 parts of dispersed sodium. About nation being separate and distinct. The low neutraliza- 10% yield of C dibasic acids was obtained. tion equivalents of the reaction products indicate that they EXAMPLE 10 are essentially C dicrarboxylic acids from the carbonation of butadiene dimerization products. An unexpected Preparation of C10 dmclds usmg phenanthrene and superior yield of 80 to 90% based on the butadiene of An experiment similar to that of Example 6 was carthese low molecular weight diacid products was obtained.

Reaction conditions Product analysis Percent Run Carbonation yield on No. Sodium, percent Butadiene Conditions Distilbump excess over Aromatichydro- Solvent Time, lable Neut. dlene theory carbon min. acids, equiv.

Grams Rate grns.

1 1,000 Ethylene glycol 107 All at start. 138 Separate step, 0.627 g. 2 Trace dimethyl ether. COz/min. 2 1,000 do 108 0.5 gJmin-.. 216 SeIparate step, Dry 1 Trace ce. 1.000 Dimethylether 127 0.5 gJmin-.. 252 do 5.4 142 2.3 4 1,000 do 108 0.5g./mln--. 250 Simultaneous, 002..-- 5 2.3

a. 5.-- 1,000 6g.paraterphenyi do 103 0.37 g./min.- 278 Separate step, Dry b. 46.6 152.9 24.6 (5.8%). Ice. 0. 39.1 270.4 20.7 a. 13.2 397.2 5.3 6. 1.000 6g.paraterphenyl do 142 0.63 g./min 226 do a. 45.2 207.0 18.0 (4.2 c. 84.0 511.7 33.6 7-.. dispersed Na. Orthoterphenyi..- do 27 0.1 gJmin--- 300 do 44.5 107 90 8- 12(1)q dispersed Paraterphenyl do 27 0.1 g./min 300 40. 6 111 83 1 The theoretical neutralization equivalent for C10 dibasic acids is 101, and the molecular weight is 202. 9 The major product from the butadiene was white, polymeric rubber acids.

ried out using 2 parts of phenanthrene instead of paraterphenyl and 46 parts of dispersed sodium. A 51% yield of C diacids resulted.

EXAMPLE 11 Comparative studies on conditions A series of comparative experiments was done in a critical study of the process. Butadiene was the diolefin employed in all these runs. The details of the operation and the results obtained are shown in the table below.

In runs No. 1 to 4, inclusive, massive bulk sodium metal was used in conjunction with various of the active others including both ethylene glycol dimethyl ether and dimethyl ether. The reaction temperature in runs 3 to 8, inclusive, was 25 to 30 C., and about 0 C. in runs 1 and 2. The solid sodium surface was exposed in the reaction mixture throughout the reaction period with the sodium surface being continuously abraded by forcing the sodium piece against a wire brush. In runs No. 1 to 3, inclusive, a separate carbonation step was carried out EXAMPLE 12 Attempted use of sodium-terphenyl complex The reaction of butadiene with a sodium-terphenyl complex was attempted. The results obtained indicate that, in the absence of metallic sodium, only unwanted byproducts were formed, and no detectable dimerization of butadiene occurred.

A solution of grams (0.5 mole) of ortho-terphenyl in 525 cc. of the diethyl ether of ethylene glycol was contacted with sodium ribbon (99 g., an excess) for a period of time. The resulting solution was decanted from the excess metallic sodium. Analysis by titration indicated that approximately 0.68 mole of sodium had combined with the 0.5 mole of ortho-terphenyl.

This ortho-terphenyl-sodium solution was diluted with an additional cc. of the diethyl ether of ethylene glycol. Butadiene (0.68 mole) was then passed into this diluted mixture over a three-hour period at a temperature of 30- C. The clear solution obtained after centrifuging was distilled to give 45 g. of a solid. The original solid was carbonated, then treated with water and free acid. Less than 0.5 g. of organic acids was obtained. An extraction with dibutyl ether gave a large amount of a crystalline solid. The total amount of solids obtained was equivalent to a practically theoretical yield of non-acid material consisting substantially of triphenylene; M. P. after recrystallization, 197-199 C.; M. P. of picrate, ZZZ-224 C.; literature values, 198.5 and 223, respectively.

From the above experiment, it is clear that the butadiene did not undergo the desired dimerization reaction in the presence of the sodium containing complex. It is evident that the presence of the alkali metal is essential for the selective dimerization of the conjugated diolefins as herein described.

What is claimed is:

1. A process which comprises selectively reacting an aliphatic conjugated diolefin with a finely divided alkali metal in an ether reaction medium of the group consisting of aliphatic monoethers having a methoxy group and an oxygen to carbon ratio of not less than 1:4 and polyethers derived from an aliphatic polyhydric alcohol having all the hydroxyl hydrogen atoms replaced by alkyl groups and mixtures thereof in the presence of a small amount, based on the weight of the diolefin, of a polycyclic aromatic hydrocarbon at a temperature below about C., thereby selectively forming the corresponding dialkali metal derivatives of unsaturated hydrocarbon dimers of said diolefin.

2. A process, as defined in claim 1, wherein the diolefin contains from four to eight carbon atoms, the alkali metal is finely dispersed sodium and the polycyclic aro matic hydrocarbon is present in an amount of from about 0.1 to about 10 weight percent based on the diolefin.

3. A process, as defined in claim 1, wherein the polycyclic aromatic hydrocarbon is selected from the group consisting of para-terphenyl, ortho-terphenyl, naphthalene, phenanthrene, and mixed terphenyls.

4. A process, as defined in claim 1, wherein the aliphatic conjugated diolefin is selected from the group consisting of butadiene, isoprene, and methyl pentadiene.

5. A process, as defined in claim 1, wherein the ether is dimethyl ether.

6. A process for selective preparation of disodio dimers of butadiene which comprises reacting a butadiene containing stream with finely dispersed sodium having an average particle size of below about 50 microns in a reaction medium consisting substantially of dimethyl ether in the presence of from about 0.1 to about 10 weight percent, based on the butadiene, of a polycyclic aromatic hydrocarbon at a temperature below about 0 C., thereby selectively forming disodio dimers of butadiene.

7. A process for selective preparation from an aliphatic conjugated diolefin of dialkali metal salts of aliphatic unsaturated diacids having two more carbon atoms per molecule than a dimer of the diolefin which comprises an initial step of reacting an aliphatic conjugated diolefin with a finely divided alkali metal in an ether reaction medium of the group consisting of aliphatic monoethers having a methoxy group and an oxygen to carbon ratio of not less than 1:4 and polyethers derived from an aliphatic polyhydric alcohol having all the hydroxyl hydrogen atoms replaced by alkyl groups and mixtures thereof in the presence of a small amount, based on the weight of the diolefin, of a polycyclic aromatic hydrocarbon at a temperature below about 0 C. thereby providing a reaction mixture comprising selectively formed dialkali metal derivatives of the unsaturated hydrocarbon dimers of said diolefin, and in a subsequent step carbonating dialkali metal derivatives produced in said initial step and unseparated from said reaction mixture to convert said derivatives to the corresponding dialkali metal salts of aliphatic unsaturated dicarboxylic acids having two more carbon atoms per molecule than a dimer of said diolefin.

8. A process, as defined in claim 7, wherein the carbonating step is carried out at below about 0 C.

9. A process, as defined in claim 7, wherein the diolefin contains from four to eight carbon atoms, the alkali metal is finely dispersed sodium, the polycyclic aromatic hydrocarbon is present in an amount of from about 0.1 to about 10 weight percent based on the diolefin, and the carbonation step is carried out at below about 0 C.

10. A process, as defined in claim 7, wherein the polycyclic aromatic hydrocarbon is selected from the group consisting of para-terphenyl, ortho-terphenyl, mixed terphenyls, naphthalene and phenanthrene.

11. A process, as defined in claim 7, wherein the aliphatic conjugated diolefin is selected from the group consisting of butadiene, isoprene, and methyl pentadiene.

12. A process, as defined in claim 7, wherein the ether is dimethyl ether.

13. A process for selective preparation from butadiene of disodio salts of C aliphatic unsaturated diacids which comprises an initial step of reacting a butadiene containing stream with finely dispersed sodium having an average particle size of below about 50 microns in a reaction medium consisting substantially of dimethyl ether in the presence of from about 0.1 to about 10 weight percent, based on the butadiene, of a polycyclic aromatic hydrocarbon at a temperature below about 0 C. thereby providing a reaction mixture comprising selectively formed disodio derivatives of dimers of butadiene, and in a subsequent step contacting with carbon dioxide disodio derivatives of dimers of butadiene produced in said initial step and unseparated from said reaction mixture at a temperature below about 0 C. to convert said derivatives to disodio salts of aliphatic unsaturated C dicarboxylic acids.

14. A process, as defined in claim 13, wherein the polycyclic aromatic hydrocarbon is selected from the group consisting of para-terphenyl, ortho-terphenyl, naphthalene, diphenyl and phenanthrene.

References Cited in the file of this patent UNITED STATES PATENTS 2,019,832 Scott Nov. 5, 1935 2,171,868 Scott et al. Sept. 5, 1939 2,352,461 Walker June 27, 1944 2,773,092 Carley et al. Dec. 4, 1956 FOREIGN PATENTS 23,727 Great Britain of 1900 OTHER REFERENCES Hansley: Ind. and Eng. Chem, vol. 43 (1951), pgs. 1759-66. 

7. A PROCESS FOR SELECTIVE PREPARATION FROM AN ALIPHATIC CONJUGATED DIOLEFIN OF DIALKALI METAL SALTS OF ALIPHATIC UNSATURATED DIACIDS HAVING TWO MORE CARBON ATOMS PER MOLECULE THAN A DIMER OF THE DIOLEFIN WHICH COMPRISES AN INITIAL STEP OF REACTING AN ALIPHATIC CONJUGATED DIOLEFIN WITH A FINELY DIVIDED ALKALI METAL IN AN ETHER REACTION MEDIUM OF THE GROUP CONSISTING OF ALIPHATIC MONOETHERS HAVING A METHOXY GROUP AND AN OXYGEN TO CARBON RATIO OF NOT LESS THAN 1:4 AND POLYETHERS DERIVED FROM AN ALIPHATIC POLYHYDRIC ALCOHOL HAVING ALL THE HYDROXYL HYDROGEN ATOMS REPLACED BY ALKYL GROUPS AND MIXTURES THEREOF IN THE PRESENCE OF A SMALL AMOUNT, BASED ON THE WEIGHT OF THE DIOLEFIN, OF A POLYCYCLIC AROMATIC HYDROCARBON AT A TEMPERATURE BELOW ABOUT O* C. THEREBY PROVIDING A REACTION MIXTURE COMPRISING SELECTIVELY FORMED DIALKALI METAL DERIVATIVES OF THE UNSATURATED HYDROCARBON DIMERS OF SAID DIOLEFIN, AND IN A SUBSEQUENT STEP CARBONATING DIALKALI METAL DERIVATIVES PRODUCED IN SAID INITIAL STEP AND UNSEPARATED FROM SAID REACTION MIXTURE TO CONVERT SAID DERIVATIVES TO THE CORRESPONDING DIALKALI METAL SALTS OF ALIPHATIC UNSATURATED DICARBOXYLIC ACIDS HAVING TWO MORE CARBON ATOMS PER MOLECULE THAN A DIMER OF SAID DIOLEFIN. 